1. Field of the Invention
This invention relates to a device for alternating scan backgrounds and for facilitating the shading correction of a scanner. In particular, the device provides more than one background color and is capable to alternate the background colors of the scanner. Such, The device provides an optical module of the scanner with scan lines of different shades to adjust the shade value of the optical module.
2. Description of the Prior Art
Conventionally, a flatbed scanner comprises a mobile optical module which move linearly for scanning. When the scanning is in process, the moving optical module captures optical signals of a plurality of scan lines of an original document. An optical sensor of the optical module then produces a scan image based on the acquired scan information.
For an original document with binder holes or lacerations, black image emerge on its scan image at the positions corresponding to the binder holes or the edges of the scan image if the scanner has a black scan background. To solve this problem, the state of the art utilizes a white scan background.
Another solution for the aforementioned problem is to design a dual scan background including a black scans background and a white scan background. The optical module is driven to move to a position underneath the selected background color and capture image information when the moving original document passes over the optical module. However, since a moveable optical module is required for the transformation of background, this solution is only applicable to a flatbed scanner in combination with a document feeder, as claimed in U.S. Pat. No. 6,166,394. The solution disclosed in said US patent requires the position adjustment of the optical module in accordance with the positions of the background and, thus, makes the positioning of the optical module difficult.
A flatbed scanner is applicable for itself or combines with a sheet feeder with an optical module for duplex scanning. However, for a scanner with dual optical modules, the optical modules of the scanner are fixed during the scanning process. If the optical module position corresponding to different background colors changes when performing shading correction, the angles and distances between the optical modules and the original document will be different from those during the scanning process; in result, the scan image using the correction values is defected. Therefore, to ensure best image quality while implementing the background alternation, the best way is not to move the optical module in order not to altering the optical path of the signals which carry the image information.
In addition, with the conventional device, the fixed optical module is not capable of capturing a plurality of scan lines, so the result of this shading correction is questionable. According to U.S. Pat. No. 6,323,933, the optical module on top of the scanner body is capable of capturing a plurality of scan lines of a calibration sheet on the optical module moving underneath the scanner. However, the said patent does not solve the problem that the distance between the upper and the lower optical modules may be different from the distance between the original document and the upper optical module. As a result, the optical path length may be different in the two circumstances and, thus, the accuracy of the shading correction is affected.